Long Term Evolution (LTE) Advanced is a mobile telecommunication standard proposed by the 3rd Generation Partnership Project (3GPP) and first standardised in 3GPP Release 10. In order to provide the peak bandwidth requirements of a 4th Generation system as defined by the International Telecommunication Union Radiocommunication (ITU-R) Sector, while maintaining compatibility with legacy mobile communication equipment, LTE Advanced proposes the aggregation of multiple carrier signals in order to provide a higher aggregate bandwidth than would be available if transmitting via a single carrier signal. This technique of Carrier Aggregation (CA) requires each utilised carrier signal, that is to say radio frequency signal, to be demodulated in a receiver at a wireless communications terminal, whereafter the message data from each of the signals can be combined in order to reconstruct the original data. Carrier Aggregation can be used also in other radio communication protocols such as High Speed Packet Access (HSPA).
Carrier Aggregation may involve aggregation of radio frequency signals, that is to say carriers that are transmitted in the same operating frequency band, or aggregation of radio frequency signals that are transmitted in different operating frequency bands. An operating frequency band may be a range of radio frequencies allocated to an operator as a contiguous block, or part of a contiguous block, and typically a radio receiver for receiving a radio frequency signal will have a receiver filter, such as a front end band pass filter, arranged to encompass the operating frequency band, but reject signals transmitted in other bands. The receiver filter serves to protect the receiver from saturation, blocking and interference by out of band signals, which may be at a high power level and beyond the operator's control.
If data is transmitted using carrier aggregation of radio frequency signals that are transmitted in the same frequency band, typically a single receiver filter may be used to receive the carrier aggregated signals, and a receiver chain for each of the radio frequency signals may be arranged to receive signals that have passed through the receiver filter. However, if data is transmitted using carrier aggregation of radio frequency signals that are transmitted in different frequency bands, more than one receiver filter is typically required to receive the carrier aggregated signals, and each receiver chain typically needs to be arranged to receive signals that have passed through the appropriate receiver filter.
A wireless communications terminal may be required to be reconfigurable between a configuration for receiving data that is transmitted using carrier aggregation of radio frequency signals in the same operating frequency band, and a configuration for receiving data that is transmitted using carrier aggregation of radio frequency signals in different operating frequency bands. A reconfigurable radio frequency circuit is required for use in such a wireless communications terminal, to allow appropriately filtered signal paths having required radio frequency performance to be configured between one or more antennas and receive chains used to receive respective radio frequency signals, which may have been transmitted in the same or different operating frequency bands.
Furthermore, a wireless communications terminal may be required to be configured to receive signals from different base stations in different operating frequency bands simultaneously for use in handover, and may also be required to receive services other than cellular radio, for example satellite navigation and or signals of an alternate radio access technology in further operating bands. The terminal may also be required to be configured for use in multi-SIM (Subscriber Information Module) operation, in which data or paging signals may be received using several carriers, each carrier typically relating to a SIM or USIM (Universal Subscriber Information Module), the carriers being in either the same or different operating frequency bands.
Conventionally, a receiver may be arranged to receive signals in a selected one or more of several operating frequency bands by the provision of a variety of receiver filters, one or more of which may be selected according to the operating frequency band in which signals are to be received. Conventionally, each receiver filter is connected to a respective amplifier such as a Low Noise Amplifier (LNA) which is designed to operate in the pass band of the receiver filter. As a result, in a system with a large number of selectable receiver filters, there may also be a large number of amplifiers provisioned, not all of which may be required to operate simultaneously for the reception of an expected set of signals. The provision of such amplifiers may lead to an increase in the number of circuit elements and complexity of a radio frequency circuit, and to increased demands for area in a radio frequency integrated circuit (RFIC) implementation.
It is an object of the invention to address at least some of the limitations of the prior art systems.